JP2004510061A - Method for selective metallization of dielectrics - Google Patents

Abstract

The present invention relates to a method for selectively metallizing a dielectric. In accordance with the present invention, an activated coating of a conductive material is applied to a dielectric and then patterned by laser treatment, thereby producing a composite of discrete conductive patterns, which is then metallized by electrolysis. Can be. The method according to the invention applies in particular to electronic components such as circuit boards. With the method according to the invention, precise patterning in the range of less than a few μm is possible, as a result of which a high placement density and high quality of the conductive paths formed by the method according to the invention is achieved.

Description

[0001]
The present invention describes a method for selective metallization of dielectrics as applied to electronics. The products made in this way are, for example, circuit boards, wiring components, chip carriers, interposers, lead frames or even whole assemblies. Hereinafter, the prior art will be described mainly with an example of manufacturing a circuit board.
[0002]
A circuit board is a wiring support that has a wiring pattern (usually a circuit printed with a copper thin film produced by a printing method) on an insulating base / substrate and serves to hold components. . The configuration of such a circuit board is various, and the substrate includes one having rigidity, flexibility or flexibility, one with or without through holes, one with or without interlayer connection. Depending on the position and number of wiring levels, it is called a single-sided circuit board, a double-sided circuit board, or a multilayer circuit board. The last one is also called multi-rare. There are also known three-dimensional circuits in which a circuit pattern extends at two or more levels.
[0003]
For example, for the production of circuit boards, various methods have been known for many years, in various forms (eg, Gunter Hermann, "Handbook of Circuit Board Technologies", Eugen Leutze, 1982, D-88348. Saulgau). The simplest first embodiment starts with a copper-coated dielectric with a positive print formed by screen printing or photographic techniques as the desired conductor pattern. This positive print acts as a protective film (etching resist) in a subsequent etching step. Exposed copper areas that are not protected by such an etching resist are removed using a suitable etchant. Copper corroded by etching is generated as waste. Next, the etching resist is stripped with an organic solvent or an inorganic solvent.
[0004]
In another embodiment of this so-called depolarization method, a negative printing of a conductor pattern is first formed as a plating resist on the dielectric to be metallized by screen printing or photographic technology. The conductive pattern is then plated by applying conductive paths to the desired thickness (usually copper). The area where the conductor pattern does not extend is protected by the plating resist. Next, a metal resist formed as, for example, a tin film or a tin-lead film is applied on the metalized conductor pattern. This coating protects the conductor pattern during subsequent depolarization (etching) of the first copper coating. Next, the metal resist is removed. Other configurations are also known. It should be pointed out, however, that this method is not suitable for forming fine or ultrafine conductor tracks (less than 50 μm). This is because the etching acts not only on the vertical direction but also on the side surface of the conductor pattern to be formed in the horizontal direction. This is a phenomenon called so-called undercut, and has technical disadvantages such as edge damage and electrical short-circuiting. The thicker the copper film removed by etching, the stronger the degree of undercut.
[0005]
To avoid the problem of partial undercut, a semi-addition method is often used. It uses an uncoated substrate on which a thin conductive plating film, typically copper deposited without external current, is applied. Subsequent processing is substantially similar to the above-described method, except that a so-called positive etching resist is not applied. That is, it is reinforced by copper plating only in a desired range of the circuit board. The copper regions of different thicknesses are then etched away by the amount of copper plating without an initial external current. Therefore, even in this method, copper is generated as waste. In addition, great care must be taken with regard to the very uniform film thickness distribution of the copper deposited by electrolysis.
[0006]
The total addition method completely eliminates the need for copper etching because copper can be applied only to necessary places such as conductor patterns and lands. Therefore, this method also has a wide field of application. Due to the lack of contact possibilities, copper plating is performed without external current. In most cases, the uncoated dielectric is coated with an adhesion-promoting or activating coating containing a catalytic species to initiate copper plating without external current. After covering all areas that should not be copper plated with a screen printing or photographic mask, the deposit and / or activator is opened to allow direct connection of copper plating without external current.
[0007]
The mask for forming the discrete conductive paths can be formed by a screen method or a photographic technique. What is common to both is that a separate mask must be created for each conductive path pattern to be formed. When a pattern is formed using a photographic process, a so-called “photoresist” must be applied as a photosensitive material to a dielectric to be metallized. Then, exposure is performed only in a specific range representing a desired positive or negative conductive path depending on a substance to be used.
[0008]
Along with the conductive path patterning by photographic methods, in particular, for three-dimensional parts, for example, in so-called molded interconnect parts, the use of an immersion tin film and patterning with a laser is considered. In this case, the use of a laser constitutes an additional step in the depolarization method. The disadvantage is that, above all, the time costs for patterning are high. The tin coating must have a thickness that provides sufficient etch protection, while the coating must be as thin as possible to ensure rapid laser ablation.
[0009]
Methods for stripping extremely thin metal films are already used today in manufacturing processes for making circuit boards. In most cases, one starts with a tin film applied to the copper, which is laser patterned and then the remaining copper is removed in an etching step (E. Tadic, "Fine patterns for future product formation" SMT 1- 2/2000, 12th edition).
[0010]
Regarding a three-dimensional body, a method of forming an ultrafine pattern using a laser technique has already been known. For example, a method for metallizing a thermoplastic for 3D-MID by a laser-assisted addition method is described. In this method, starting from doped plastics, these plastics can be activated by laser and then are suitable for metallization without current for the formation of conductive paths (SMT 4/2000, 20th edition).
[0011]
Other methods of laser ablation of various metal coatings are also known. D. The method described by Meier peels the gold thin film by mask projection with an ultraviolet laser and then strengthens it without current ("Laser Patterning of Fine Lines" Fifth Annual Meeting of Flexible Materials, Denver / USA 1999, proceedings Record). In particular, laser peeling of an organic film doped with palladium is also known (J. Kickelhain: Doctoral dissertation, University of Rostock, 1999). However, a disadvantage common to all these methods is that, following laser patterning, metallization by a currentless addition method is performed to strengthen the conductive path pattern.
[0012]
In addition, conductive polymers have been gaining importance in the metallization of dielectrics for some time. It is used in particular in the so-called direct plating method for interlayer connection and fabrication of two-layer circuit boards and multilayer circuit boards. This is a depolarization method in which the dielectric is activated with the respective conductive polymer and then metallized by direct plating (PCT / EP89 / 00204). The disadvantage is that the conductivity of the conductive polymer is relatively low, especially in planar metallization.
[0013]
There is also known a method of proposing selective metallization by direct plating based on a conductive polymer. For example, US Pat. No. 5,953,405 discloses a method of coating a substrate with a primer and a conductive polymer. A lithographically patternable plating resist is used to form the pattern. After plating, the resist is first stripped off, and then the conductive polymer under the resist is removed. The disadvantage in this case is the use of a lithographically patternable plating resist. This is due to the high demands placed on clean room technology and the subsequent removal of the conductive polymer required to achieve fine or ultra-fine patterns.
[0014]
It is an object of the present invention to provide a method for selectively metallizing a dielectric material, which enables precise patterning in a range smaller than μm and eliminates the need to use a resist each time. It is to provide a simple, reliable, inexpensive and environmentally friendly method.
[0015]
The technical solution provided by the method according to the invention is that the dielectric to be metallized is coated with a conductive activation film which adheres and then the desired conductive path pattern is formed from this film by means of a precision tool laser. It is. The remaining pattern of the activated film continues to be conductive, and when current is applied, metallization by electrolysis, preferably copper plating, can be performed without problems by conductive coupling. By doing so, patterning in a range of less than 50 μm is also possible.
[0016]
Therefore, the method of the present invention advantageously overcomes the limitations of the prior art. According to the invention, several measures are proposed for the method which make it technically advantageous, very economical and effective. Hereinafter, this method will be described based on an example of manufacturing a circuit board, but this method is not limited to the electronic field.
[0017]
According to a first solution, when a current is applied according to the method of the invention, electrolytic plating is enabled by fixing a thin conductive activation film to the dielectric to be metallized. This conductive activation film enables electrolytic plating.
[0018]
The activation film may be formed in various forms as long as sufficient conductivity is guaranteed. Advantageously, polymerized or copolymerized pyrrole, furan, thiophene and / or their derivatives can be used. It is particularly advantageous to use conductive polymers based on polythiophene derivatives (DMS-E). In addition, metal sulfides and / or polymetal sulfides, and Pd and / or copper catalysts can be used. Furthermore, there is a possibility that a thin metal film can be applied to the substrate. In this case, for example, a copper film can be applied in various ways.
[0019]
It is advantageous to apply a thickness of the activation coating in the range of about 0.1 μm. The method according to the invention advantageously discloses the possibility of patterning the conductive activation coating to produce a discrete conductive pattern. For this purpose, a new approach is proposed by the present invention. According to a particularly advantageous feature of the invention, the precise patterning of the activation film is performed by means of a laser. Patterning, i.e., formation of a conductor pattern, can be performed after the application of a conductive polymer, after the application of a metal sulfide and / or a polymetal sulfide, after the application of a Pd catalyst and / or a copper catalyst, or the application of a metal thin film. Can be done after wearing. The remaining pattern of the activated coating continues to be conductive and can be metallized by electrolytic plating as long as there are conductive path bonds. In this case, the insulated area can be connected to an artificial conductor complex using a so-called auxiliary conductor. The conductor pattern remaining from the activation film is metallized by applying an external current in a subsequent electrolytic plating step. For the electroplating of the patterned activation film, various metal electrolytes can be used in the present invention, but a copper electrolyte is particularly preferred. This makes it possible, with laser ablation, to advantageously and precisely form conductive paths in the range of a few μm. In addition, the method according to the invention makes it possible to remove, after metallization, the so-called auxiliary conductors which, during metallization, bridge a kind of current between insulated conductive path areas. The destruction of the artificial conductive path composite can also be performed by, for example, laser treatment.
[0020]
It is therefore advantageous that the method according to the invention opens up the possibility of eliminating the need for metallizing baths without external currents, for example used in addition processes. Under such circumstances, environmental pollution due to chemical residue and chemical wastewater can be suppressed to a low level. In addition, metal films deposited by external currents are clearly inferior in ductility to much finer crystalline and denser metal films formed electrolytically. The fact that the method according to the invention allows direct electrolytic plating by the application of an external current on the basis of the activated coating ensures that the sleeve or edge is damaged by the thermal load of the soldering process, for example, when mounting the conductor substrate later. It is advantageously ensured that the high ductility requirements needed to be avoided are met.
[0021]
The method according to the invention also encompasses the possibility of metallization by external currents, if necessary and desirable. To be implemented, the adhered activated coating is adapted for metallization without external current so that the activated coating contains the catalyst species required for copper plating without external current and is compatible with the appropriate treatment. There must be.
[0022]
A special feature of the method according to the invention for conducting track patterning with a laser offers the further advantage of forming the track quickly and individually. As a result, manufacturing flexibility is increased by being able to react quickly, for example, when changing the conductive path pattern. This is achieved, for example, by the fact that, unlike all known methods, no screen masks, photomasks or other types of masks for defining the contours of the conductive paths are required. This is because the contour of the conductive path is formed by the laser.
[0023]
Furthermore, the method according to the invention uses all kinds of resist materials, for example to form a mask or to protect the conductive path pattern by a depolarization method, etc., based on the fact that a conventional photomask can be dispensed with. Is unnecessary. This saves both chemicals and work steps, since they do not have to be applied or subsequently removed.
[0024]
Furthermore, the advantage is disclosed that there is no risk that the metallization will be rough due to accurate laser patterning. By doing so, it is guaranteed that the conductive path is formed accurately, and as a result, the reject rate can be kept low.
[0025]
The density of the conductor patterns achievable with the method according to the invention, the arrangement density on the circuit board, and its high quality and precision are characteristics of the advantages of the method according to the invention. Because of the need to save the weight and volume of the electronics and to optimize the working speed, very short conductive paths are required. Therefore, the method according to the invention is particularly suitable for producing products that require a high degree of integration. This also applies, for example, to applications in computer technology, communication technology, connection technology or medical technology. Further, according to the method of the present invention, a three-dimensional circuit requiring a circuit pattern of two or more levels can be produced without any problem.
[0026]
The laser used in the method according to the invention can be, for example, a KrF laser, a XeC1 laser or a Nd-YAG laser. Further, another laser may be used as long as the required precise laser peeling can be performed.
[0027]
The method according to the invention also discloses the possibility of special control of the laser, for example allowing the equipment to be connected to any kind of control module. This control module may be, for example, a computer.
[0028]
The method according to the invention offers the advantage that less copper is consumed in metallization than conventional methods, because the copper is applied only in the required places by means of precise patterning. . Further, from this situation, the etching process and the stripping process can be almost unnecessary, so that the consumption of chemical substances is reduced. These features of the method according to the invention ultimately lead to advantageous cost savings and also to a reduction of the environmental burden due to the reduction of chemical waste.
[0029]
Furthermore, a significant advantage of the process technology over all methods based on photochemical processes is that the method according to the invention makes it possible to obviate all shading measures. By using a laser, there is no need to provide a special storage space or working room for the photosensitive photoresist.
[0030]
Other advantages and features are evident from the following examples which illustrate the method of the invention.
Example 1
An uncoated substrate (eg, BR4) is coated with a conductive polymer according to the DMS-E method. Therefore, the working steps described below are performed.
1. Conditioner (Brazolit V) 3min 40 ° C
2. Manox (KMnO ₄ / H ₃ BO ₃ ) 2 minutes 40 ° C
3. Monopole TC (Catalyst fixation) 4 minutes Room temperature X) Laser patterning: Laser type: Nd-YAG (3 times frequency)
, Pulse / position: 1.
[0031]
Example 2
An uncoated substrate (eg, BFR4) is coated with a conductive polymer according to the DMS-E method. The work steps described in Example 1 (steps 1 to 3) are performed and the following work steps are added.
[0032]
4. Conditioner PE 3 minutes Room temperature 5. Ultraplast 2000 (Pd catalyst) 4 minutes 40 ° C
6. Generator (Cu-containing solution) 5 minutes 63 ° C
This is followed by the next working phase.
X) Laser patterning: Laser type: KrF
Wavelength: 248 nm, energy density on substrate: 100 mJ / cm ² , laser energy: 450 mJ / cm ² , pulse / position: 2.
[0033]
Example 3
The substrate is coated with copper, applied with a special resist for SBU circuits (eg, LDN 9056 from Enthone) and processed as described below.
1. Swelling agent 10 minutes 80 ° C
2. KMnO ₄ alkali 13 minutes 80 ° C
3. Remover Mn (sulfuric acid, H ₂ O ₂ ) 2 min Following the working steps above room temperature, the substrate is treated as described in Example 2.
Example 4
An uncoated substrate (eg, FR4) is treated as follows.
1. 1. Plato solution for 14 minutes at room temperature Plate solution 3 2 minutes Room temperature 3. Plato solution 14 minutes Room temperature 4. Plate solution 34 minutes Room temperature (X) Laser patterning: laser type: KrF, wavelength: 248 nm, energy density on substrate: 150 mJ / cm ² , laser energy: 450 mJ / cm ² , pulse / position: 1.
[0034]
Example 5
Substrates coated with copper and provided with a special resist for SBU circuits (eg, LDN 9056 from Enthone) are treated as described below.
1. Swelling agent EL (organic alkali swelling agent) 10 minutes 80 ° C
2. KMnO ₄ alkali 13 minutes 80 ° C
3. Remover Mn (sulfuric acid, H ₂ O ₂ ) 2 minutes Room temperature 4. 4. Plate solution 14 minutes Room temperature 5. Plate solution 3 2 minutes Room temperature 6. Plate solution 14 minutes Room temperature 7. Plate solution 3 2 min room temperature X) Laser patterning: laser type: KrF, wavelength: 248 nm, energy density on substrate: 180 mJ / cm ² , laser energy: 490 mJ / cm ² , pulse / position: 2.
[0035]
Example 6
An uncoated substrate (eg, FR4) is treated as follows.
1. Conditioner (Brazolit V) 3 minutes 40 ° C
2. Manox (KMnO ₄ / H ₃ BO ₃ ) 2 minutes 40 ° C
3. Monopole TC (fastening of catalyst) 4 minutes Room temperature 4. 4. Plate solution 14 minutes Room temperature 5. Plate solution 3 2 minutes Room temperature 6. Plate solution 14 minutes Room temperature 7. Plater solution 32 minutes room temperature X) Laser patterning: laser type: KrF, wavelength: 248 nm, energy density on substrate: 200 mJ / cm ² , laser energy: 450 mJ / cm ² , pulse / position: 1.
[0036]
Example 6a
It is also possible to modify the work process so that the work steps are performed as follows. First, processing steps 4 to 7 are performed, and then processing steps 1 to 3 are performed. Thereafter, processing step X) laser pattern shaping is performed.
[0037]
Example 7
A substrate coated with copper and provided with a special resist for an SBU circuit (eg, LDD9056 from Enthone) is treated as follows.
1. Swelling agent EL (organic alkali swelling agent) 10 minutes 80 ° C
2. KMnO ₄ alkali 13 minutes 80 ° C
3. Remover Mn (sulfuric acid, H ₂ O ₂ ) 2 minutes room temperature, followed by working steps 1 to X of Example 6.
Example 7a
Here, too, the working process can be changed so that the processing steps are performed as follows. First, processing steps 4 to 3 are performed. The processing steps 4 to 7 of Example 6 are followed by the processing steps 1 to 3 of Example 6. Thereafter, processing step X) laser pattern shaping is performed.
[0038]
Example 8
An uncoated substrate (eg, FR4) is treated as follows.
1. Conditioner (Brazolit V) 3 minutes 40 ° C
2. Manox (KMnO ₄ / H ₃ BO ₃ ) 4 minutes 80 ° C
3. Catalyst (organic monomer) 2 minutes Room temperature 4. Fixing (Example: Organic acid) 2 minutes Room temperature X) Laser patterning: Laser type: XeCl
Wavelength: 308 nm, energy density on substrate: 120 mJ / cm ² , laser energy: 450 mJ / cm ² , pulse / position: 1.
The following processing steps can be performed before laser patterning.
5. 5. Conditioner PE 3 minutes Room temperature 6. Ultraplast 2000 (Pd catalyst) 4 minutes 40 ° C
7. Generator (Cu-containing solution) 5 minutes 63 ° C
[0039]
Example 9
The substrate coated with copper and provided with a special resist for an SBU circuit (for example, LDD9056 from Enthone) is treated as follows.
1. Swelling agent EL (organic alkali swelling agent) 10 minutes 80 ° C
2. KMnO ₄ alkali 13 minutes 80 ° C
3. Remover Mn (sulfuric acid, H ₂ O ₂ ) 2 minutes Room temperature This is followed by processing steps 1 to 4 of Example 8, followed by laser formation. It is possible to carry out working steps 5 to 7 before the laser formation.
As a variant, the processing steps can be changed as follows.
1. Swelling agent EL (organic alkali swelling agent) 10 minutes 80 ° C
2. KMnO ₄ alkali 13 minutes 80 ° C
3. Remover Mn (sulfuric acid, H ₂ O ₂ ) 2 minutes Room temperature 4. 4. Plate solution 14 minutes Room temperature 5. Plate solution 3 2 minutes Room temperature 6. Plate solution 14 minutes Room temperature 7. Plate solution 3 2 minutes Room temperature 8. Conditioner (Brazolit V) 3 minutes 40 ° C
9. Manox (KMnO ₄ / H ₃ BO ₃ ) 4 minutes 80 ° C
10. Catalyst (organic monomer) 2 minutes Room temperature 11. Fixing (example: organic acid) 2 minutes room temperature
Prior to laser formation, the following operational steps can optionally be incorporated into the process flow.
12. Conditioner PE 3 minutes Room temperature 13. Ultraplast 2000 (Pd catalyst) 4 minutes 40 ° C
14． Generator (Cu-containing solution) 5 minutes 63 ° C
After the laser formation, the following subsequent processing is performed.
The circuit board is electroplated with a commercially available copper and / or nickel electrolyte until the conductor pattern on the circuit board is completely metallized. By the above method, it is possible to realize a conductor pattern and a conductive path interval of several μm.

Claims (14)

In the method of selectively metallizing dielectrics, each dielectric is coated with an activation film made of a conductive material so as to be fixed, and the activation film is patterned by a subsequent laser treatment to form discrete conductive films. A method for selectively metallizing a dielectric, comprising creating a pattern and then metallizing it. The method of claim 1 for use in making parts or assemblies in electronics. The method according to claim 1, wherein the method is applied to manufacture of a circuit board. 4. The method according to claim 1, wherein the dielectric is plastic and / or ceramic. The method according to claim 1, wherein an activation film made of a conductive polymer is applied. The method according to claim 5, wherein a polymerized or copolymerized pyrrole, furan, thiophene and / or a derivative thereof is used as the conductive polymer. 6. The method according to claim 5, wherein poly-3.4-ethylene-dioxyoffen is used as the conductive polymer. The method according to claim 5, wherein the conductive polymer is further coated with a Pd species and / or a Cu species. 5. The method according to claim 1, wherein the activation coating comprises a metal sulfide or a polymetal sulfide. 10. The method according to claim 1, wherein the activation coating comprises a thin metal coating. The method according to any one of claims 1 to 10, wherein the metallization is performed by an electrolytic method. 12. The method according to claim 1, wherein a copper electrolyte is used for metallization. 13. The method according to claim 1, wherein a KrF laser, a XeC1 laser or a Nd-YAG laser is used for patterning the activation film. 14. The method according to any one of the preceding claims, wherein the conductive pattern is destroyed following metallization.